The phrase "doeth justice to" generally means "to do something well or to give it the credit it deserves." Antonyms for this phrase could include "discredit," "dishonor," or "ignore." If someone fails to do justice to a certain task, they could be said to have discredited it or dishonored it by not putting in the necessary effort or by doing a poor job. Similarly, if someone ignores a particular accomplishment or fails to acknowledge its significance, they could be said to have not done justice to it. However, doing justice to something is a positive expression, and its antonyms imply the opposite.